This invention relates to the art of thermal recording apparatus using a thermal head.
Thermal recording materials comprising a thermal recording layer on a substrate such as a film, which are hereunder referred to as thermal materials, are commonly used to record the images produced in diagnosis by ultrasonic scanning.
This recording method, commonly referred to as thermal image recording, eliminates the need for wet processing and offers several advantages including convenience in handling. Hence, the use of the thermal image recording system is not limited to small-scale applications such as diagnosis by ultrasonic scanning and an extension to those areas of medical diagnoses such as CT, MRI and X-ray photography where large and high-quality images are required is under review.
As is well known, thermal image recording involves the use of a thermal head having a glaze in which heat-generating elements for heating the thermal recording layer of a thermal material to record an image are arranged in one direction and, with the glaze a little pressed against the thermal material (thermal recording layer), the thermal material is relatively moved in the auxiliary scanning direction perpendicular to the main scanning direction in which the glaze extends, as the respective heat-generating elements of the glaze are heated imagewise by energy application to heat the thermal recording layer, thereby accomplishing image reproduction.
Not only the thermal recording apparatus but also various other image recording apparatus including laser printers and plate-making apparatus are adapted to perform sharpness compensation in order to produce high-quality, clear and well modulated images by means of edge enhancement for improved image sharpness. In practice, however, the sharpness of recorded images is affected by various factors which, in the case of thermal recording, include the temperature of the thermal head, the recording speed (auxiliary scanning transport speed) and the gamma value of the thermal material used. Stated specifically, the image sharpness deteriorates with the increasing temperature of the thermal head (heat-generating elements) and with the increasing recording speed (the speed of movement of the thermal head relative to the thermal material) but with the decreasing gamma value of the thermal material and the recorded image will look blurred if these phenomena occur. More specifically, as for the recording speed, the image sharpness in the auxiliary scanning direction deteriorates with the increasing recording speed, and the image sharpness in the main scanning direction deteriorates with the decreasing recording speed, and the recording image will look blurred, if there phenomena occur. Among others, the increase in the temperature of the thermal head is most influential in the sharpness of the recorded image.
The reduced sharpness of the recorded image will lead to the deterioration of the quality of finished images and can be a serious problem in applications that require the recording of high-quality images. In the above-stated medical applications, images of particularly high quality are required and the reduction in sharpness is an obstacle to the viewing of the correct image, potentially leading to a wrong diagnosis.